Two former Parramatta Eels players are accused of harbouring semi-automatic weapons and possessing more than half-a-million dollars in cash after dramatic arrests in Sydney's Centennial Park yesterday.

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John Bergamin remains a suspect in Ms Bergamin's disappearance. Ms Bergamin's body has never been found.

Her estranged husband John Bergamin and eldest son, Stephen Bergamin- who has since changed his surname to Zanin- remain suspects in the case, police said today.

John Bergamin was charged with Ms Bergamin’s murder in 2006, but was later released due to a lack of evidence.

In April this year, a highly-detailed anonymous letter, which also asked for indemnity from prosecution, was sent to Victoria Police.

"You need to contact us, because you hold the key to potentially solving this matter," Missing Persons Squad Detective Inspector Tim Day said.

"It's clear from the letter the author has intimate details of what has happened, of who the offenders may be and intimate details of where Kath's remains might be."

Det. Insp Day said anyone with information should consider their position.

Kate Bergamin is believed to have been abducted 15 years ago.

"(Perhaps) through naivety and false pretences, the innocence of youth, they've been roped into certain events that at the time the gravity of which may not have been obvious to them," he said.

"Experience has shown us as investigators, that when we finally catch up with the principal offender, they attempt to mitigate and minimise their own culpability, often by throwing the non-principal offender under the bus."

There is a $1 million reward and the possibility of indemnity from prosecution for information that solves the case.

"It would end the torment of this whole thing," Mr Russell said of his sister's murder being solved.

Ms Bergamin split from her husband and moved off their Cheshunt farm in the months before her disappearance.

The couple had a "deeply troubled relationship" and Mr Bergamin would regularly resort to behaviour to deliberately frighten his wife, Coroner Peter White found in 2008.

Both John and Stephen Bergamin were excused from giving evidence at the inquest on the grounds they should not be compelled to give evidence that could incriminate themselves.